The present invention relates to a plate resonator for wide band damping in rooms, e.g., enclosed, relatively small rooms, e.g., 4.times.5 m.sup.2 and 3 m high.
Sound damping measures in enclosed rooms have hitherto served primarily two completely different goals: (1) that of obtaining the best possible transmission between the sound source and the listeners ("room acoustics"), and (2) the least possible influence of the sound sources on the affected workplaces ("noise control").
In the first instance, the aim is to allow sound to occur as naturally, unaltered and effectively as possible, whereas in the second instance the aim is to change the noise spectrum of sound as much as possible-provided its volume can be sufficiently reduced. In addition to these traditional fields of activity for acoustic experts, there is a third domain increasingly attracting the attention of builders and planners: (3) the inverse effect of small rooms on sound (in particular at low frequencies) and the related detrimental effects of a very different nature on especially high-quality workplaces.
Poor intelligibility of speech and major sound distortion can greatly negatively affect the working conditions of, e.g., speakers, musicians, teachers and sound engineers. This inverse effect of some rooms makes it very difficult for musicians playing together to hear and control themselves, thus forcing them to play louder. In small, improperly damped rooms, e.g., vaulted basements, (but also partially roofed orchestra pits), the sound level can build up to a hearing-impairing volume level far above 100 dB(A).
In the transmission function of a rectangular, e.g., 5.times.4.times.3 m.sup.3 room in an undamped, unfinished state of construction exposed to constant airborne noise excitation there are volume differences of up to 40 dB between the maximum and minimum at any point of emission or reception. If one takes into consideration that in a real situation the transmission function of a room, as depicted in FIG. 1 covering a bass instrument, it becomes evident that a room can interfere considerably if its natural resonance is ignored. As non-uniform as the frequency dependence of an entire room is, the spatial distribution of the intensity of the sound field at a specific frequency is just as uneven (cf. FIG. 2). However, the fade away behavior of a room during an emission break at frequencies between two resonance peaks is perceived by sensitive ears as very unpleasant vibrations. Sound altering "distortions" ranging from the familiar "droning" of speech or music make the work of demanding artists and sound engineers all too frequently unnecessarily difficult.
This problem, however, is also widespread, in a less intense form, in auditoriums, conference rooms, and living rooms if they are only sparsely furnished. Only in these cases, however, users with lesser schooled ears are often unable to articulate the reason for their discomfort in such rooms. The fact that in some rooms a thin layer of, e.g., mineral fibers, has been installed, with the best of intentions, behind perforated plates on parts of the ceiling, does not solve the problem. Retrofitted mounting of structured high-resilient foam boards is also not really successful and sometimes even intensifies the problem at low frequencies.
Thus, a sound-absorbing multi-layer board having holes on the front side with a hole/surface ratio of at least 5% is known from German Patent document DE 74 27 551 U1. Sound absorbing plastic foam is arranged behind this multi-layer board. Furthermore, a similar arrangement having an internal layer of gypsum board or an asbestos board is known from U.S. Pat. No. 3,215,225. However, the front plate is also partially designed in a reflecting manner with a damping coat similar to an antidrone coat in passenger vehicles.